The present invention relates to a sealing method for sealing a package housing products such as electronic devices or the like, a sealing apparatus, and to a packaged product to be manufactured by the sealing method.
In recent years, fine electronic components have been highly in demand with the miniaturization of electronic devices. For example, in a crystal oscillator module, a crystal oscillator is mounted to a thin case and thereafter is sealed with a lid. The module as a packaged product is to be manufactured. As for sealing method, seam welding has been employed in general and soldering has been also used.
However, the above sealing methods have been with the following problems.
(1) Case of seam welding:
As welding medium, Kovar ring is used. Kovar should be molded into a shape of ring or anything else, which leads to increasing the manufacturing cost.
Welding speed is slow and thus the productivity is rather limited.
An apparatus for seam welding usually is expensive.
Seam welding is not suitable for small sized packages because it is really a task to realize a welding apparatus that works precisely for such miniaturized packages.
(2) Case of soldering by electron beam heating:
It is very likely that thermal damage is given to cases usually made of ceramics and as a consequence cracks may be generated in those cases.
A pressure mechanism for fixing the lid and the case to be welded tends to be rather complex because these elements need to be fixed in a way that never interferes with the electron beam for welding.
(3) Case of soldering by heating the whole case:
When the whole case is heated, a crystal oscillator is also heated. For this reason, there is the possibility that the frequency of the oscillator may be shifted after sealing.
The present invention has been made in order to solve the above problems. The objective of the present invention is to provide a package sealing method and a package sealing apparatus that improves the productivity and the reliability of packaging products without compromising the performances of packaged products.
In order to achieve the above object, the present invention provides a package sealing method comprising the following steps of: interposing a bonding member between a case housing a product and a lid made of material that transmits a laser beam used for sealing; irradiating the bonding member with the laser beam through the lid so that the bonding member is melted; and welding the case and the lid together via the bonding member. The bonding member is formed on the case or the lid and thereby the sealing can be carried out efficiently and effectively.
According to the above method, the following effects can be obtained.
(1) welding portions of the case and the lid are locally heated using the laser beam, and thereafter, the bonding member is melted so that the case and the lid are welded together. Therefore, heat can hardly be conducted to the packaged product. Accordingly, it is possible to prevent any deterioration in the performances of the packaged product by heat and thus improve the reliability of the packaged product.
(2) An irradiation energy of the laser beam is controlled with high accuracy and therefore the optimal condition for welding is easy to obtain. Further, the lid that is highly transparent for the laser beam is used and so that the energy for sealing can be very effectively utilized.
(3) Unlike seam welding, no undesired trace due to welding is left and therefore the appearance of package can never be harmed.
The case and the lid are fixed together by pressuring one to the other. Also they are fixed together by vacuum chucking one to the other through a hole attached to the case. After the case and the lid are fixed, a metal is placed in the hold and then a laser beam is focused onto the metal so that it can be melted to seal the hole. By doing so, the sealing is completed without giving any thermal damage to the product packaged in the case, and thus the reliability of the product is never jeopardized.
Not only welding the case and the lid but also sealing the hole attached to the case can be done using the same laser beam wavelength. Therefore, a single laser beam irradiation apparatus may be used in common for both processes and the whole sealing apparatus can be simplified.
For welding the case and the lid, the laser beam may be focused and scanned on the bonding member point by point. Moreover, the laser beam is transmitted through a phase hologram so that a diffraction light pattern is generated and thereafter the diffraction light pattern may concurrently strike every point of the bonding member.
According to the above irradiation method of scanning a laser beam, the laser beam is steered by a relatively simple means. On the other hand, according to the method using a phase hologram, the incident light can be efficiently used and the welding may be quickly performed with a good uniformity of weld quality and that greatly contributes to the improvement of the packaging productivity.
With the above phase hologram in use, some light energy can be reserved in the zero-th order diffracted beam and the diffraction light pattern can be positioned by referring to the location of the zero-th order diffracted beam.
Moreover, the laser beam for sealing the package is focused with a condensing lens while the phase hologram is arranged between the condensing lens and the lid and thereafter the position of phase hologram is decided on the optical axis such that a diffraction light pattern from the phase hologram can be obtained with its desired dimensions. Because of this scheme, a suitable optical pattern for welding the case and the lid can be readily obtained.
A temperature distribution over a weld portion of the case and the lid is monitored during the irradiation of laser beam to the bonding member, and thereby the irradiation conditions are suitably adjusted in accordance with the temperature of the weld portion. Therefore, welding the case and the lid together can always be performed appropriately by knowing the actual on-site conditions.
Further, the bonding member is preheated, and thereafter is irradiated with the laser. By doing so, it is possible to save both time and energy needed to complete the packaging.
An electronic device module can be manufactured by packaging an electronic device in the case using the above method.
Moreover, in order to carry out the above method, the present invention provides a sealing apparatus for welding a case housing a product and a lid together by a bonding member, comprising: a fixing means for fixing the case and the lid; and a laser beam irradiation apparatus for irradiating the bonding member with a laser beam.
As fixing means, a pressure apparatus is used and besides it is possible to use a vacuum chucking apparatus for fixing the lid to the case using a hole formed to the case. Further, the sealing apparatus may be provided with a laser beam irradiation apparatus for melting a metal arranged in the hole formed to the case.
The sealing apparatus of the present invention may be provided with a laser scanner for sequentially irradiating the bonding member with a laser, or a phase hologram for concurrently irradiating every point of the bonding member with a diffraction light pattern of laser beam.
Further, the sealing apparatus of the present invention may be provided with a temperature monitor for monitoring a temperature distribution over a weld portion of the case and the lid during the irradiation of the bonding member with a laser.
Furthermore, the sealing apparatus of the present invention may be provided with a heater for preheating the bonding member to be irradiated with a laser beam.
With these apparatuses, the aforementioned methods can be implemented and manufacturing the packaged products can be conducted with the expected advantages.